Influence of lactic acid on the catalytic performance of MDABCO for ring-opening polymerization of L-lactide

A series of metal organic frameworks (MOFs) MDABCO (M = Co, Ni, Cu, Zn; DABCO = 1,4-diazabicyclo[2.2.2] octane) are utilized as catalysts for the bulk ring-opening polymerization of L-lactide. The catalytic activity varies in the order CuDABCO, NiDABCO < ZnDABCO, CuDABCO. By adding lactic acid, we unexpectedly observed enhanced catalytic activity. The combined use of lactic acid and ZnDABCO during polymerization results in a highly active polymerization system, along with the gradual change of MOFs structure caused by an increased acid concentration. Compared to related homogeneous fragments, such as zinc nitrate and 1,4-diazabicyclo [2.2.2]octane, ZnDABCO is found to afford highly isotactic polylactide, which would be ascribed to the unique structural properties of MOFs.